Preheat oven to 300 degree F. Place egg whites and cream of tartar in teh bowl of a stand mixer. Using a wire whisk, beat over medium high speed.

Egg whites will stiffen while being beaten, and stick to the spatula when scooped. Add the 1 cup sugar a little at a time. Add vanilla. Increase speed to high and continue beating egg whites until stiff but not dry. The texture should be smooth and silky. Do not over beat as this will make the mixture separate and become watery.

Grease jelly roll pan. Line pan with waxed or any brown paper; or you can use nonstick baking paper. Grease paper laid out on pan (if using waxed or brown paper).

Spread and level beaten egg whites on pan.

Press hard with the spatula on the egg whites to remove air. To further remove air bubbles, lift the pan a few inches above the table and let it drop. Do this once or twice.

Immediately place pan in the oven and bake for 30 to 40 minutes until mearingue is firm to the touch and turns light brown.

While meringu is baking, cook the filling. Place egg yolks and condensed milk in a doube boiler. If not using a double boiler, fill the bigger saucepan halfway with water. Place the smaller sauceapn, with the yolks and mil, on top. Make sure the bottom of the smaller pan does not touch the water. Cook over low heat, stirring continuously until mixture is thick, about 40 minutes. Constant stirring creates a smooth, lump free consistency.